Iguazú and Iguaçu Falls: A Shared River, Forest and Borderland

For most of its course the Iguazú River runs quietly west across southern Brazil, broad and brown and island-studded. Then, a little over twenty kilometres before it meets the Paraná, it reaches the edge of a basalt plateau and drops away along a front almost three kilometres wide. Iguazu Falls (Iguazú in Spanish, Iguaçu in Portuguese) is usually described as one of the world’s great waterfalls, and it is, but it is better understood as a shared landscape: one river, two national parks and a single block of subtropical forest divided by an international border. On Days 20 and 21 of our South American Small Group History and Culture Tour, the group sees the falls first from Brazil and then from Argentina, and the difference between the two days is a large part of the point.

One river, two national perspectives

The name comes from Guaraní and means, simply, “great water”. The river rises in the Serra do Mar near Curitiba and flows about 1,320 kilometres inland before joining the Paraná at the point where Argentina, Brazil and Paraguay meet. For its final stretch the Iguazú itself is the border: Argentina’s province of Misiones on the south bank, Brazil’s state of Paraná on the north.

The first European known to have seen the falls was the Spanish explorer Álvar Núñez Cabeza de Vaca, who reached them in 1541. For centuries afterwards they were remote from any capital. What made them a national question on both banks was the twentieth century’s interest in frontier, sovereignty and scenery. Argentina created Iguazú National Park in October 1934. Brazil followed with Iguaçu National Park in January 1939, two decades after the aviator Alberto Santos-Dumont visited in 1916 and argued that the falls should be held as public land.

UNESCO inscribed the Argentine park as a World Heritage site in 1984 and the Brazilian park in 1986, both for their natural beauty and for the importance of their habitats. Together the two parks protect around a quarter of a million hectares. The modern crossing between them is the Tancredo Neves Bridge, opened in 1985 between Foz do Iguaçu and Puerto Iguazú. Paraguay’s Ciudad del Este lies a short distance away, and the three cities together form the region known as the Triple Frontier.

How Iguazu Falls formed: basalt, steps and retreating water

The falls are cut into some of the largest lava fields on Earth. Around 130 million years ago, as South America and Africa began to pull apart, repeated eruptions spread flood basalts across more than a million square kilometres of what is now Brazil, Argentina, Paraguay and Uruguay. At Iguazú the pile is roughly a kilometre thick, built from successive lava flows, and at least eleven of them are exposed in the cliffs around the falls.

Waterfalls on rock like this do not stay in one place. The river undercuts the softer layers, the harder lip above eventually collapses, and the falls creep upstream. Geologists estimate that Iguazú has worked its way back about 23 kilometres from the Paraná confluence, leaving the steep-walled canyon below the falls as the record of its retreat.

The result is a waterfall front of around 2.7 kilometres, broken by forested islands into many separate cascades. Britannica and most guidebooks count about 275, though the number genuinely changes with the river: at low water some falls disappear entirely, and at high water neighbours merge. Individual drops reach roughly 80 metres. Most of the falls, close to four in five by the usual reckoning, are on the Argentine side of the border.

The centre of the whole system is the Devil’s Throat, Garganta del Diablo in Spanish and Garganta do Diabo in Portuguese. Here the main channel of the river funnels into a narrow, U-shaped chasm and falls on three sides into a cloud of spray so dense that the bottom is rarely visible.

The forest that frames the falls

The water draws the eye, but UNESCO listed both parks as much for their forest as for their falls. They protect one of the largest remaining blocks of the interior Atlantic Forest, known in Argentina as the Selva Paranaense. This is a different forest from the Amazon: subtropical rather than tropical, and once far more extensive across Brazil, Argentina and Paraguay. Brazil’s national space research institute and the SOS Mata Atlântica foundation estimated in 2026 that only about a quarter of its original cover survives, and only around an eighth as mature forest. At Iguazú it still runs unbroken across the border.

Walk any trail in either park and the structure is plain: slender palms, strangler figs, tree ferns, bromeliads and orchids on the branches, lianas looping between trunks. Argentina’s National Parks Administration records about 450 bird species in its park alone, among them toucans. UNESCO’s citations add rarer animals that visitors are unlikely to see, including the harpy eagle, tapir, ocelot, giant anteater and broad-snouted caiman. Even the falls themselves are habitat. Great dusky swifts nest on the wet rock beside and behind the curtains of water, and they are known for flying straight through the falling water.

The forest’s most closely watched animal is the jaguar, called yaguareté in Argentina and onça-pintada in Brazil. In the mid-2000s only around forty were thought to survive across the whole protected corridor around the parks. Since then Argentine and Brazilian researchers have run joint camera-trap censuses across both countries, and the 2024 count estimated between 64 and 110 animals. A fourteenth binational census, using around 250 camera traps, began in March 2026 and runs into 2027. Visitors will almost certainly never see one; the point is that the population is counted at all, and counted across a border.

Conservation has also meant hard decisions. In 1999 UNESCO placed the Brazilian park on its List of World Heritage in Danger after a road through the park, the Estrada do Colono, was illegally reopened. It was removed from the list in 2001 once the road was closed again.

Brazil’s panorama, Argentina’s close-up

Because most of the falls sit on the Argentine side, the two parks offer opposite experiences of the same water. From Brazil you look across the canyon at the Argentine falls, which is why the Brazilian side is known for the panorama. From Argentina you walk among, above and below the falls themselves.

On the Brazilian side, a single trail of roughly a kilometre and a half follows the canyon rim through forest, opening onto one viewpoint after another along the Argentine front. It ends at a walkway that runs out over the river towards the Devil’s Throat, and a panoramic lift links the walkway with the viewpoints above. On the tour this is the first afternoon, after arriving from Buenos Aires, combined with a visit to the Parque das Aves, a private bird park beside the national park entrance that cares for Atlantic Forest species, many of them rescued from the illegal wildlife trade.

The next morning the group crosses the Tancredo Neves Bridge into Argentina. Here the park is laid out as a series of walkways. The Upper Circuit runs level along the lip of a line of falls, so that the water slides away just below your feet. The Lower Circuit drops down to the base of the cliffs, closer to the noise and spray. A small forest railway carries visitors to the start of the Devil’s Throat walkway, which runs for about a kilometre over the wide upper river to a platform at the edge of the chasm.

Which side of Iguazu Falls is better, Argentina or Brazil?

Neither, because they show you different things, and seeing both is the reason to spend two days rather than one. The Brazilian side gives the overview, the sense of the whole curved front at once, and suits a shorter, gentler walk. The Argentine side gives scale and detail, standing on top of individual falls and at their foot, and takes most of a day. Seeing Brazil first, as the tour does, means you understand the shape of the system before walking into it.

Will you get wet at Iguazú Falls?

Almost certainly, and on the boat safari, thoroughly. The included boat trip on the Argentine day uses a twin-engine craft built for the river, which runs up the lower canyon through several rapids and close in to the base of the falls; passengers are expected to be soaked. Bring a light waterproof or buy a disposable poncho, and keep cameras in a dry bag. The walkways nearest the Devil’s Throat and the base of the Lower Circuit also carry heavy spray when the river is high.

A river managed upstream: dams, droughts and floods

Iguazú is not a wild river in the way it looks. Upstream in Paraná state, the Iguaçu is dammed for hydroelectric power at a series of large plants, and UNESCO notes that water levels at the falls are partly regulated by them. Upstream hydropower is listed among the continuing pressures on the Brazilian site.

Even so, the river’s natural swings are enormous. In an ordinary month around 1,500 cubic metres of water pass over the falls each second. In June 2014 the flow reached roughly 45,000 to 47,000 cubic metres a second, the highest on record. In late October 2023 a flood of about 24,000 cubic metres a second, sixteen times normal, swept away the Argentine Devil’s Throat walkway, which stayed closed for about nine months until it was rebuilt in July 2024. At the other extreme, in May 2020 the river fell to its lowest level on record, and in March 2026 low water forced a suspension of the boat trips.

The 2026 El Niño has been a reminder of how quickly conditions change. As a precaution, Argentina dismantled its Devil’s Throat walkway in August 2026, with reopening not expected before December. In mid-October the flow passed 12,000 cubic metres a second; the Brazilian walkway closed, and for several days some of the Argentine circuits were shut while others reopened as the water allowed.

What happens if the river is too high or too low?

The parks close walkways and suspend boat trips when the flow makes them unsafe, sometimes at a day’s notice, and reopen them once engineers have checked the structures. Which trails are open on a given day cannot be promised in advance. Your Program Leader works around closures on the spot, using whichever circuits, viewpoints and the Brazilian panorama trail are open; even at its most restricted, the falls at very high water are a remarkable sight.

How much walking does a visit to Iguazú Falls involve?

Expect two full days on your feet, on a tour rated Level 3, Moderate to Challenging, which can involve up to six hours of activity a day. Most walking is on raised metal walkways and paved paths, often wet. On the Argentine side the Upper Circuit and the Devil’s Throat walkway have no stairs, while the Lower Circuit includes flights of steps; the Brazilian trail also has stairs, with the panoramic lift as the step-free option. Coatis roam the paths on both sides and are bold around food: feeding them is prohibited, and they can bite.

Do you need a visa for the Brazilian side of Iguazú Falls?

Australian, United States and Canadian citizens currently do, even for a day visit. Brazil reintroduced visas for these nationalities in April 2025, issued as an electronic visa applied for online in advance, and it cannot be obtained at the border. On this tour the visa is needed regardless, since the group stays on the Brazilian side at Iguazú and finishes in Rio de Janeiro. Australians do not need a visa for tourist visits to Argentina. Requirements change, so check Smartraveller or your government’s advice before you book; our guide to Argentina and Brazil travel advice covers the wider practicalities.

Between the Andes and the Atlantic

On the tour, Iguazú is the hinge between two halves of South America. The first three weeks climb from the Pacific coast into the Andes, the Altiplano and Bolivia, then come down to the European grandeur of Buenos Aires, where the group visits the Teatro Colón and the opera house’s civic history. Iguazú returns the journey to forest and water before the Atlantic finale in Rio de Janeiro. It also answers the Amazon days near the start of the tour: our account of the Tambopata National Reserve and the Madre de Dios describes a tropical river forest that makes a revealing comparison with the subtropical forest here.

Seen in that sequence, the falls are more than a natural spectacle. They are a frontier that two countries chose to protect from opposite banks, a forest managed by two park services, and a river whose moods are counted in cubic metres a second. Our overview of the 25-day South America cultural tour route shows how Iguazú fits among Machu Picchu, Lake Titicaca and the cities, and the South American Small Group History and Culture Tour brings them together with a Program Leader, local guides and a small group of up to 16 travellers.